STROUD Worked examples and exercises are in the text Programme 10: Sequences PROGRAMME 10 SEQUENCES

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Difference equations Limits of sequences

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Difference equations Limits of sequences

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Sequences Graphs of sequences Arithmetic sequences Geometric sequences Harmonic sequences Recursive prescriptions

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Sequences Any function f whose input is restricted to positive or negative integer values n has an output in the form of a sequence of numbers. Accordingly, such a function is called a sequence.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Graphs of sequences Since the output of a sequence consists of a sequence of discrete numbers (the terms of the sequence) the graph of a sequence will take the form of a collection of isolated points in the Cartesian plane. For example, consider the sequence defined by the prescription

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Arithmetic sequences Consider the sequence 2, 4, 6, 8, 10,... where each term is obtained from the previous term by adding 2 to it. Such a sequence is called an arithmetic sequence. In its general form an arithmetic sequence is given by a prescription of the form: The number a is the first term because it is the output from the function when the input is n = 0. The number d is called the common difference because it is the difference between any pair of successive terms and, despite being called a difference it is in fact the number that is added to a term to find the next term in the sequence.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Geometric sequences Consider the sequence 2, 4, 8, 16, 32,... where each term is obtained from the previous term by multiplying it by 2. Such a sequence is called a geometric sequence. In its general form a geometric sequence is given by a prescription of the form: The number A is the first term because it is the output from the function when the input is n = 0. The number r is called the common ratio because it is the ratio between any pair of successive terms – it is the number that a term is multiplied by to find the next term in the sequence.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Harmonic sequences A sequence of terms is said to be an harmonic sequence if the reciprocals of its terms form an arithmetic sequence. Accordingly, the sequence defined by the prescription is an harmonic sequence.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Recursive prescriptions A prescription of a sequence where each term of the sequence is seen to depend upon another term of the same sequence is called a recursive prescription and can make the computing of the terms of the sequence more efficient and very amenable to a spreadsheet implementation. For example, from the prescription It can be seen that Is the recursive prescription.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Recursive prescriptions Notice that by itself the recursive prescription Is of little use because we do not know how to start it off. We need additional information in the form of an initial condition. Since then

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Difference equations Limits of sequences

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Difference equations Limits of sequences

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Solving difference equations Second-order, homogeneous equations The particular solution

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Solving difference equations The recursive prescription can be written as In this form it is an example of a first-order, constant coefficient, linear difference equation also referred to as a linear recurrence relation. It is linear because there are no products of terms such as f (n+1)f (n), it is first-order because f (n+1) is just one term away from f (n), and it has constant coefficients (the numbers multiplying the as f (n) and as f (n+1) are constants and do not involve n).

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Solving difference equations The order of a difference equation is taken from the maximum number of terms between any pair of terms so that, for example: is a second-order difference equation because f (n+2) is two terms away from f (n).

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Solving difference equations We have seen how the prescription for a sequence such as: can be manipulated to create the difference equation: What we wish to be able to do now is to reverse this process. That is, given the difference equation we wish to find the prescription for the sequence which is the solution to the difference equation.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Solving difference equations Consider the difference equation: To find the form of the general term f (n) that satisfies this equation we first assume a solution of the form: where K and w are non-zero real numbers and n is an integer.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Solving difference equations If we substitute this form for f (n) into the difference equation we find that: This gives us the characteristic equation: This means that We shall, therefore, write the solution as:

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Solving difference equations Using the initial term f (0) = 6 it is then found that: And so:

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Second-order, homogeneous equations The solution to a second-order, homogeneous difference equation follows the same procedure with the exception that the characteristic equation has two roots and so a linear combination of two solutions is required as well as the application of two initial conditions. For example, the difference equation Gives rise to the characteristic equation and hence the solution

STROUD Worked examples and exercises are in the text Programme 10: Sequences Difference equations Equal roots of the characteristic equation If the roots of the characteristic equation are equal then a different form for the solution must be given.. For example, the difference equation Gives rise to the characteristic equation and hence the solution

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Difference equations Limits of sequences

STROUD Worked examples and exercises are in the text Programme 10: Sequences Functions with integer input Difference equations Limits of sequences

STROUD Worked examples and exercises are in the text Programme 10: Sequences Limits of sequences Infinity Limits Infinite limits Rules of limits Indeterminate limits

STROUD Worked examples and exercises are in the text Programme 10: Sequences Limits of sequences Infinity There is no largest integer; this fact is embodied in the statement that the integers increase without bound – no matter how large an integer you can think of you can always add 1 to it to obtain an even larger integer. An alternative description of this idea is to say that the integers increase to infinity where infinity is represented by the symbol ∞ (negative infinity is represented by −∞). Unfortunately, because we have a symbol for it there is a temptation to give infinity some numerical aspect that it does not possess. It must be clearly understood that although infinity is a well- established concept it cannot be defined numerically and so it cannot be used as a number in any arithmetic calculations.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Limits of sequences Limits The number that the output of a sequence approaches as the input increases without bound is called the limit of the sequence. For example, no matter how large n becomes never attains the value of 0. However, it can become as close to 0 as we wish by choosing n to be sufficiently large. We call 0 the limit of as n approaches infinity and write

STROUD Worked examples and exercises are in the text Programme 10: Sequences Limits of sequences Infinite limits Sometimes as n becomes large so does f (n). For example, the output from the sequence becomes large even faster than n does. In this case we write the limit as: Be aware. This notation can be misleading if it is not correctly understood. It does not mean what it appears to mean, namely that the limit is equal to infinity. It cannot be equal to infinity because infinity is not numerically defined so nothing can be said to be equal to it. What it does mean is that as n becomes large without bound then so does n 3. If a sequence has a finite limit it is said to converge to that limit. If a sequence does not have a finite limit it is said to diverge.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Limits of sequences Rules of limits Multiplication by a constant The limit of an expression multiplied by a constant is the constant multiplying the limit of the expression: where k is a constant.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Limits of sequences Rules of limits Sums and differences The limit of a sum (or difference) is the sum (or difference) of the limits:

STROUD Worked examples and exercises are in the text Programme 10: Sequences Limits of sequences Rules of limits Products and quotients The limit of a product (or quotient) is the product (or quotient) of the limits:

STROUD Worked examples and exercises are in the text Programme 10: Sequences Limits of sequences Indeterminate limits Sometimes when trying to determine the limit of a quotient the limits of both the numerator and the denominator are infinite. Such a limit is called an indeterminate limit and cannot be found without some manipulation on the quotient.

STROUD Worked examples and exercises are in the text Programme 10: Sequences Learning outcomes Understand the nature of probability as a measure of chance Compute expectations of events from an experiment with a number of outcomes Assign classical measures to the probability and be able to define the probabilities of both certainty and impossibility Distinguish between mutually exclusive and mutually non-exclusive events and compute their probabilities Compute conditional probabilities Evaluate permutations and combinations Use the binomial and Poisson probability distributions to calculate probabilities Use the standard normal probability distribution to calculate probabilities